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Acid-Base Theories ( pp 623-625)

CLASSICAL REACTIONs overview (continued) . Acid-Base Theories ( pp 623-625). Modern Theory: Try #1Svante Arrhenius: Father of the first modern acid / base theory. Thesis on Acids & Bases derided by his research committee…. Graduates with Ph.D ordinare ( no distinction).

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Acid-Base Theories ( pp 623-625)

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  1. CLASSICAL REACTIONs overview (continued) Acid-Base Theories (pp623-625) Modern Theory: Try #1Svante Arrhenius: Father of the first modern acid/base theory Thesis on Acids & Bases derided by his research committee… Graduates with Ph.Dordinare (no distinction) Young Arrhenius Old Arrhenius (wins Nobel prize for same acidbase theory)

  2. CLASSICAL REACTIONs OVERVIEW(continued) A measure of this Ph.D `ordinaire’’s brilliance… In 1896 Arrhenius predicted the green house gas (CO2) from profligate burning of the the newly popular fuel source …petroleum oil… would cause (gasp !) measurable and catastrophic global warming… …starting in 1990-2000 AD …the entire scientific establishment (and Standard Oil) laughed at him (again)

  3. FYI…. Not a single current Republican member of the US Congress has yet to admit that global warming is caused by burning of fossil fuels.

  4. CLASSICAL REACTIONs overview(continued) 1) Arrhenius Model =OH-donor BASE =H+ donor ACID HF HCl HBr HNO3 HClO4 H2SO4H2CO3 H3PO4 NaOHKOH NH4OH Ca(OH)2Mg(OH)2 Al(OH)3 Fe(OH)3

  5. CLASSICAL REACTIONs (continued) Acid-Base reactions ala’ Arrhenius: A+B= neutral HCl(aq) + NaOH(aq) NaCl(aq) + H2O H2SO4 + Mg(OH)2 MgSO4(aq) + 2H2O General rule for Arrhenius acid-base ACID+BASE= SALT + WATER

  6. CLASSICAL REACTIONs OVERVIEW continued) The `Inconvenient Truth’ about the Arrhenius model: basic salts EXAMPLE: Na2CO3 (sodium carbonate) No H+ or OH-….=> salt only

  7. CLASSICAL REACTIONs OVERVIEW(continued) The `Inconvenient Truth’ about the Arrhenius model: basic salts (continued) EXAMPLE: Na2CO3 (sodium carbonate) experimental results of adding to water: • Turns pink in presence of phenolphthalein • gas-forming reaction with HCl, pink disappears Where’s OH ??? => A base !!!!?????

  8. CLASSICAL REACTIONs OVERVIEW (continued) The `Inconvenient Truth’ about the Arrhenius model: basic salts (continued) Other examples of `basic’ salts Na3PO4 K2SiO3 NaC2H3O2 Basic salts cannot be rationalized using Arrhenius’ acid/base model

  9. CLASSICAL REACTIONs (continued) Bronstedto the rescue… Winner of the Bronsted look alike contest…. Young Bronsted…Swedish chemist circa 1910… Young James Dean…American actor circa 1955…(“Rebel Without a Cause,”“East of Eden”, “Giant” ) Bronsted a few years after marriage and kids

  10. CLASSICAL REACTIONs OVERVIEW(continued) BronstedModel of Acids/Bases3new concepts (see pp 452-453 & 623-6) New Concept #1: Follow the protons Acid= proton donor (=H+) No real change from Arrhenius HF, HCl, HBr HNO3 HClO4 H2SO4 H2CO3 H3PO4 ARRHENIUS ACIDS = BRONSTED ACIDS

  11. CLASSICAL REACTIONs OVERVIEW(continued) BRONSTED’S MODEL OF ACIDS/BASES: New Concept #1: following the protons (cont.) BASE= proton acceptor Examples of Bronsted Bases OH- CO3-2 ,PO4-3, C2H3O2-,SiO3-2… The set of Bronsted bases includes Arrhenius bases + …. …nearly any negative ion (=anion) that even weakly attracts protons

  12. CLASSICAL REACTIONs OVERVIEW(continued) BRONSTED’S MODEL OF ACIDS/BASES:New Concept #2 How the proton acceptor creates the basic salt effect: Hydrolysis…Bronsted bases `split’ water !!! EXAMPLE CO32- + H-OH  HCO3- + OH- Hydrolysis reaction ..Bronsted Base is basic in water because it splits water to make OH-!

  13. BRONSTED’S MODEL OF ACIDS/BASES:New Concept #3a: conjugate acid/basepairs Conjugate idea is like going drag… Men=acid Women=base Identify `acids’ and bases CONJUGATE ACID CONJUGATE BASE BASE ACID

  14. CLASSICAL REACTIONs OVERVIEW(continued) BRONSTED’S MODEL OF ACIDS/BASES:New Concept #3a: conjugate acid/base pairs Identify `acid’ and base Identify conjugateacid and base Conjugate acid  HCO3- + OH- CO32- + H-OH Acid Base Conjugate base Acid conjugate base Base conjugate acid

  15. new concept #3a: Conjugates (continued) When acid and base reacts…. Acid conjugate base Base conjugate acid PO43- + HCO3- HPO42- + CO32- conjugate base conjugate acid acid base EXAMPLE: IDENTIFY ACID, BASE AND THEIR CONJUGATEBASE AND ACID ABOVE

  16. CLASSICAL REACTIONs OVERVIEW(continued) BRONSTED’S MODEL OF ACIDS/BASES:New Concept #3b: Bronsted Model ACID+ BASECONJUGATE BASE + CONJUGATE ACID • spontaneous acid + base reactions • produce weaker acids +bases Arrhenius Model ACID+ BASE SALT +WATER Both products `neutral’

  17. ACID-BASE THEORIES SUMMARIZED ARRHENIUS BRONSTED PROTON DONOR ACID = H+DONOR BASE= OH- DONOR PROTONACCEPTOR ACID +BASE  SALT + WATER CONJUGATE ACID + CONJUGATE BASE

  18. What observation required Bronsted to create a new Acid/Base Theory different than Arrhenius’s model ? • Many salts formed conjugate acids. • Spontaneous acid+base reactions only occurred if weaker acids and bases formed. • H2O spontaneously decomposed to OH- and H+ in presence of various salts. • Many salts without OH- somehow created OH- in water.

  19. Which part of the Bronsted salt K3PO4 is the proton acceptor ? • K+ • O2- • P3- • PO43- • K3PO4 • OH-

  20. What new concept of Bronsted’smostdirectly explains why many salts are bases? • The anionic part of salts can hydrolyze water. • Spontaneous acid/base reactions lead to weaker conjugate acids/bases. • Bronsted bases are proton acceptors. • Bronsted acids are proton donors.

  21. In-class reaction Jeopardy WHAT IS… Low heat, precipitates, cation swap metathesis Pick the Arrhenius acids H2O HNO3 NaHCO3HBrNaCl HNO3HBr Na2CO3 for example A Bronsted base What’s my reaction type: Acid/base neutralization (Arrhenius) HCl + KOH KCl + H2O

  22. In-class reaction Jeopardy WHAT IS… What’s my reaction type: Acid/base hydrolysis (Bronsted) K3PO4 + H2O  HK2PO4 + KOH Write my products ? AgNO3(aq) + NaCl(aq) ????? AgCl(s) + NaNO3(aq) Pick the Bronstedbase(s) NaOH NaHCO3 K3PO4 Pick the Arrhenius bases NaOHHBr NaHCO3 K3PO4 NaOH

  23. Practice with Bronsted model and language 1) Identify the Bronsted bases in this list: HBrNaOH Na2CO3NH4Cl K3PO4 NaCl base base acid base base acid 2) Identify the acid (A), base (B) and the conjugate acid (CA) and conjugate base (CB) in the two reactions below 1) Na2CO3 + H3PO4 NaHCO3 + NaH2PO4 B A CA CB 2) KCN + H2O HCN + KOH B A CB CA 3) What is the hydrolysis reaction that occurs with PO43- ? HPO42- + OH- PO43- + H2O

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